A ShutterSnitch user wrote this to me - good stuff and I thought it needed to be shared:

"To get around the iPad's inability to create "ad hoc" networks, I bought a little Aluratek battery-powered wireless router (about US $ 90) and carry it in a pocket of my camera bag. This lets me network all my devices (Eye-Fi card, WT-4, iPad, sometimes a laptop) wherever I'm photographing. Using the router actually is more convenient than using a public WiFi network -- I have pre-configured it for all my devices, so I never need to worry about changing any settings."

Most portable routers like that work fine with out a data modem. I do not know about that particular one, but I can tell you that the Cradlepoint routers work fine with out internet connection and I have used Eye-Fi Cards over many of them with out a data connection, but not ShutterSnitch though.